Staphylococcus aureus (S. aureus) is a facultative anaerobic, gram positive, spherical bacterium considered to be an opportunistic pathogen. S. aureus commonly colonizes the nose, skin and mucosal surfaces of healthy humans. Approximately 20-30% of the population is colonized with S. aureus at any given time. These bacteria often cause minor infections, such as pimples and boils in healthy individuals. Normally, mucosal and epidermal barriers (skin) protect against S. aureus infections. Interruption of these natural barriers as a result of injuries—such as burns, trauma or surgical procedures—dramatically increases the risk of infection and could cause severe and/or systemic infections. Furthermore also diseases that compromise the immune system (e.g., diabetes, end-stage renal disease, cancer, AIDS and other viral infections), but also immunosuppressive therapies—e.g. as radiation, chemotherapeutic and transplantation therapies—increase the risk of infection. Opportunistic S. aureus infections can become quite serious, causing endocarditis, bacteremia, osteomyelitis and abscess formation, which might result in severe morbidity or mortality.
S. aureus is a leading cause of bloodstream, skin, soft tissue, and lower respiratory tract infections worldwide. The frequencies of both nosocomial and community-acquired infections have increased steadily over the years. During a localized infection such as pneumonia in humans, approx. 40% of patients with S. aureus pneumonia develop blood stream infections and disseminated disease. The dissemination of the bacterial infection can lead to blood stream infection and distant organ seeding. The blood stream infection can lead to septicemia, a rapidly progressing and frequently fatal complication of S. aureus infections.
In addition, treatment of these infections has become more challenging due to the emergence of multi-drug resistant strains. In almost all developed countries, resistance to antibiotics in methicillin-resistant S. aureus strains (MRSA) is a major problem in hospitals and other healthcare settings and although data on structure and function of S. aureus proteins became more comprehensive the development of an effective vaccine remains a challenge. Notably, the incidence rate of all invasive MRSA infections, including those outside of hospitals, in comparison to other bacterial pathogens is quite high and 20% of these infections result in death. In addition the occurrence of acquired resistance to vancomycin further limited the options for treatment of severe S. aureus infections.
MprF was identified as the enzyme catalyzing Lysyl-phosphatidylglycerol (Lys-PG) biosynthesis in Staphylococcus aureus which is a major component of the bacterial membrane (Peschel et al. 2001). MprF does not only synthesize Lys-PG but also accomplishes the translocation of Lys-PG from the inner to the outer leaflet of the membrane or lipid bilayer resulting in a reduced negative charge of the membrane surface. The mortality of mice infected with a S. aureus mutant strain with an inactivated MprF gene was found to be significantly lower than that of mice infected with the wildtype strain (Peschel et al, 2001). In addition the mutant strain was cleared more efficiently from the bloodstream and showed impaired capacity to proliferate within cardiac vegetations compared to the wildtype in a model of endovascular infection of rabbits (Weidenmaier et al., 2005). Together these findings strongly support the hypothesis of a role of MprF in Staphylococcal virulence (Peschel et al., 2001).
Furthermore, in S. aureus Lys-PG and MprF also affect the susceptibility to cationic antibiotics, e.g. gentamycin (Nishi et al., 2004), and daptomycin (Ernst et al., 2009). The lipopeptide daptomycin is an approved last-resort antibiotic for the treatment of methicillin- and vancomycin resistant S. aureus. An analysis of daptomycin non-susceptible clinical strains revealed that many of them harboured point mutations in the mprF gene, which were interpreted as gain-of-function mutations (Jones et al., 2008, Peleg et al., 2012).
MprF is highly conserved within laboratory and clinically relevant strains of the species Staphylococcus aureus (FIGS. 12A and 12B). The importance of Lys-PG in resistance to antimicrobial peptides has also been demonstrated in other bacterial species. A mutant of Mycobacterium tuberculosis defective in Lys-PG production showed increased sensitivity to vancomycin and defective growth in mouse and guinea pig lungs and reduced pathology relative to wild type (Maloney et al., 2009). Deletion of an mprF-homologue in Listeria monocytogenes resulted in a strain less resistant to specific antimicrobial peptides, with reduced ability to infect macrophages and epithelial cells and the deletion mutant was attenuated in a mouse infection model (Thedieck et al., 2006). Recently a publication described that the expression of an MprF-homologue from Clostridium perfringens in a S. aureus mprF-deletion mutant restores the resistance towards daptomycin indicating a role of C. perfringens MprF in resistance to antimicrobial peptides (Slavetinsky et al., 2012).
Thus, an object of the invention is the provision of products and methods for prophylaxis and therapy of clinically complex S. aureus infection. In particular the present disclosure provides antibodies or fragments specific to MprF from S. aureus, wherein the antibody has protective capacity in vivo, against clinically complex S. aureus infection. Furthermore, the present disclosure provides antibodies or fragments specific for MprF which enhance the susceptibility of S. aureus to antimicrobial peptides and antibiotics which interfere with the bacterial membrane. Furthermore, the present disclosure provides a combinatorial therapy comprising MprF antibodies or fragments together with cationic antimicrobial peptides (CAMP) or CAMP-like antibiotics, e.g. daptomycin, for the treatment of bacterial infections.